It's just a flat amplifier with an available 26dB of gain. It was used as a generic amplifier in Neumann consoles of the era. There is a PV15, PV26 and PV46. They are not all the same circuit but they are all from the same design era.

I actually thought it had an unbalanced front end from memory and thought it might make a good unbalanced flat front end amplifier to feed the PTS base station. When I looked at it I realized it had a differential front end and thought it may work as a balanced front end like your preamplifier PCB's. The PV15 has an unbalanced input and the PV46 has a transformers balanced input. I know the front end would need a few values changed if it would work at all for an MM cart.

Here is the PV46SD line amp. This is my favorite era of Neumann design. The next era using the OA10 opamp doesn't sound as good and neither does the later IC based designs. The SP66 console I have uses them. The signal flow of the SP66 is PEV EQ-RV66 Attenuators-EE66-HT66 passive 12dB/oct HPF/LPF-PV46-Fader. All Neumann mastering consoles were offered in a rack mount or a console version. I used to have a console version with a Telefunken M10A transport. That used Neumann designed playback electronics. It used PV26's as line drivers for the tape machine. I now have a rack mount version with no tape machine.